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BAHIA BLANCA, Argentina (Reuters) - An abnormal sound detected in the South Atlantic ocean around the time that an Argentine navy submarine sent its last signal last week was "consistent with an explosion," a navy spokesman said on Thursday.

Spokesman Enrique Balbi described the blast in the morning of Nov. 15 as "abnormal, singular, short, violent" and "non-nuclear."

The navy did not have enough information to say what the cause of the explosion could have been or whether the ARA San Juan could have been attacked, Balbi told reporters.

A huge sea and air hunt is being conducted for the vessel, which had 44 crew on board when it went missing last week. The disappearance has plunged relatives of the crew members into an anguished wait for news and transfixed the South American country.

The information about the explosion received on Thursday morning was consistent with a separate report received on Wednesday of an "acoustic anomaly" in the same area and around the same time the vessel gave its last signal, Balbi said.

"This is very important because it allows us to correlate and confirm the acoustic anomaly from the U.S. report yesterday," he said.

The site of the abnormal sound was close to where the German-built vessel gave its last location, about 430 km (270 miles) off the coast.

Earlier on Thursday, a U.S. embassy spokeswoman said an object detected by a U.S. Navy plane near the area where the submarine sent its last signal turned out not to be the missing vessel. The plane, a P-8A Poseidon, was one of dozens of Argentine and foreign boats and planes involved in the hunt.

Concerns are growing that the submarine could be near the last of its seven-day oxygen supply.

Relatives of the crew members have gathered at a naval base in the coastal city of Mar del Plata, some 400 km (250 miles) south of Buenos Aires, where the search is being coordinated.

The submarine was en route from Ushuaia, the southernmost city in the world, to Mar del Plata when it reported an electrical malfunction shortly before disappearing last week.

The submarine was launched in 1983 and underwent maintenance in 2008 in Argentina. Its four diesel engines and its electric propeller engines were replaced, according to specialist publication Jane's Sentinel.